[clang] [llvm] [RISCV] Relax march string order constraint (PR #78120)

[Fangrui Song via cfe-commits]

MaskRay wrote:

> Address the https://github.com/riscv-non-isa/riscv-toolchain-conventions/pull/14
>
> This patch relax the -march string for accept any order.

Perhaps:

Follow https://github.com/riscv-non-isa/riscv-toolchain-conventions/pull/14 by dropping the order requirement of `-march`.

https://github.com/llvm/llvm-project/pull/78120